THE BRAIN OF MODERN MAN 795 



IMPRESSION GAINED FROM A SURVEY OF THE EXTERNAL SURFACE 



OF THE BRAIN 



The impression gained from a survey of the external surface of the 

 brain is that of a pronounced expansion in all those parts particularly con- 

 cerned with the functions over which the neopallium presides. Thes' 

 tions are all in the interest of neokinesis. Expansions in the pariet lor 



the increase of somesthetic sensibility enrich kinesthetic association in the 

 control of motion. Expansions of the occipital lobe extend the realm of the 

 visual sphere, not alone for sensory interpretation but equallv for those 

 contributions which vision makes to the regulation of the more highly 

 organized skilled movements. Enlargement of the temp>oraI lobe extends the 

 sphere of auditor\" perception to bring into existence those combinations of 

 neural impulses advantageous alike to the acquisition " nee 



of skilled performances; ; . the most notable expansion ot a 



the frontal lobes for the i: lii of neural svntheses essential to the orj^an- 



ization of person; ■ .e construction of judgment and of all the higher 



faculties of dis. iion and reason governing the conduct of the individual 



in adjustment to his complex environment. A similar expansion in the interest 

 of augmented function appears in the late- of the cerebellum. 



SURFACE L.\NDMARKS OF THE BRAIN STEM 



As is the case with cerebral hemisphere and cerebellum, all surface land- 

 marks become better defined in t rain stem. The ventral surface of 

 the oblongata presents a well-detined ventromedian sulcus which in its 

 more caudal p>ortions is interr terlacing libers of the 

 decussation. This decussati' l-s itself apf)arent more in man 

 than in the lower forms. On either side of the sulcus are two prominent 

 pyramids, their apices tap>ering toward the pyra \.-cussation. A marked 



